Radiant heaters convert gas, electric, or other non-radiant energy (e.g., energy stored in a fuel cell) into radiant energy. Other resulting non-radiant energy output (such as convective) diminishes heater efficiency. Other heater byproducts may contribute to air pollution. Existing radiant heaters have typically emphasized the primary radiant energy output. More particularly, they have typically disregarded the energy wasted by flue product gas flow (e.g., exhaust gasses produced from fuel combustion) and by other convective gas flow (e.g., movement of heated ambient air that results from both gas-fueled and electric-powered radiant heaters). Electric radiant heater products typically claim to be 100% efficient on the grounds that all the input electricity is converted into some sort of heat. Gas radiant heater products (such as tube heaters, for example) typically claim very high efficiency on the grounds that the wasted flue product includes low unburned chemical energy. However, existing radiant heaters unnecessarily waste an amount of radiant energy equal to the convective heat gain in the ambient and/or flue products. The present inventor has recognized a need for improving efficiency or other aspects of radiant heaters or other radiant energy systems.